Shaker-type, voltage-gated K+ (KV1) channels are an important determinant of the resting membrane potential and diameter of small cerebral arteries. During hypertension, KV1 channel-mediated dilation appears to be blunted and is postulated to increase myogenicity in the cerebral circulation. However, little is known about the mechanisms that regulate the expression of KV1 channels at the plasma membrane of cerebral vascular smooth muscle cells (cVSMCs). In this regard, we recently identified scaffolding proteins including PSD95 (postsynaptic density 95) in rat cVSMCs that have never been described. PSD95 is a well- characterized scaffolding protein in neurons with more than 50 known binding partners that can facilitate macromolecular signaling between ion channels and receptors. Subsequently we determined that KV1 channels associate with the PSD95 scaffold in cVSMCs, and that PSD95 is required for the normal expression and dilator function of KV1 channels in small cerebral arteries. Finally, we have evidence that the 21 adrenergic receptor (21AR) - another known binding partner of the PSD95 scaffold - activates a KV1 channel-mediated dilator pathway. Thus, we envision that PSD95 enables the efficient coupling of the 21AR signaling pathway to KV1 channels in cVSMCs and we have designed experiments to characterize the impact of this novel PSD95 complex on cerebrovascular reactivity. Based on our early findings, we hypothesize that: 21AR and the KV1 channels form a macromolecular vasodilator complex on a PSD95 scaffold in the rat cerebral circulation. We further propose that the down-regulation of cerebrovascular KV1 channels during hypertension disrupts the PSD95 scaffold resulting in a synchronized loss of the 21AR-KV1 signaling pathway and a vasodilator defect. These hypotheses will be tested using co-immunoprecipitation and confocal microscopy to discern protein interactions in small cerebral arteries. The physiological impact of siRNA knockdown of PSD95 or KV1 channels in cerebral arteries in vitro and in vivo will be evaluated using patch-clamp electrophysiology, microvessel reactivity assays, and intravital microscopy. The findings of this project will identify for the first time a vasodilator complex in vascular smooth muscle that is regulated by scaffolding proteins, and will set the stage for further studies to understand how ion channels are localized with their signaling partners in cVSMCs.